These are called choreic movements or chorea or it could be myoclonus depending on the kind of jerky movements that you are getting. Sleep myoclonus occurs during the initial phases of sleep, especially at the moment of dropping off to sleep. They are just a side effect of the drug. They can happen also in some healthy people as they are falling asleep (sometimes called "sleep starts"), they get involuntary jerking movements in their arms or legs and is usually not harmful, it is just a little annoying to the person experiencing them. Stop taking the medication. If it continues after you stop taking the medicine, see your doctor.